This invention relates to aqueous acidic copper plating baths, and more particularly, to aqueous acidic copper plating baths capable of depositing bright and level copper deposits over a wide current density range.
Acid copper plating baths for producing a brilliant copper finish on articles have been known in the art, and a number of patents have described various brightening agents which can be added to acidic baths. Examples of such patents include U.S. Pat. Nos. 2,707,166, 2,707,167, 2,830,014, 3,276,979 and 3,288,690. In U.S. Pat. No. 3,725,220, it has been suggested that the utilization of organic sulfonates or carboxylates as brightening additives in acid aqueous copper plating baths results in improved stability of the bath and effective deposition of copper over a satisfactory current density range.
In a number of instances in the prior art acid copper plating baths, a sufficiently brilliant finish is obtained but little or no smoothing effect on the surface is obtained. The ability of a plating bath to produce deposits relatively thicker in small recesses and relatively thinner on small protrusions thereby decreasing the depth of surface irregularities is known as "leveling." For example, a copper plating bath with satisfactory leveling ability can be utilized to reduce or eliminate the effect of microscopic cracks or scratches on the surfaces of the articles being plated. Accordingly, a number of additives have been described in the prior art for increasing the leveling effect of acid copper plating baths. For example, U.S. Pat. No. 3,101,305 describes a leveling additive obtained from the condensation of thiourea with aliphatic aldehyde such as formaldehyde. Since the additives which have been described in the prior art are useful either as brightening agents or leveling agents, it generally has been necessary to utilize two additives in acid copper plating baths, one for brighteners and another for leveling. U.S. Pat. No. 4,038,161 is an example of a patent which describes the use of two additives in acid copper plating baths. One type of brightener compound disclosed in U.S. Pat. No. 4,038,161 to be used in combination with a leveling agent is the dithiocarbamic acid derivatives of the formula EQU R.sub.1 R.sub.2 NCS.sub.2 --(CH.sub.2).sub.n --X
wherein R.sub.1 and R.sub.2 are hydrogen, aliphatic or aromatic groups, n is an integer from one to ten, and X is a hydroxyl group, a carboxyl group, a sulfonic acid group or an alkali metal salt of the carboxyl or sulfonic acid groups. U.S. Pat. No. 3,414,493 also describes brightener compositions for copper plating baths, and one of the types of brightener composition can be presented by the formula EQU R.sub.3 R.sub.4 NCS.sub.2 CH.sub.2 O(CH.sub.2).sub.n SO.sub.3 M
wherein R.sub.3 and R.sub.4 are alkyl radicals, n is an integer from 3 to 8, and M is hydrogen, sodium or potassium.
U.S. Pat. No. 4,134,803 describes nitrogen and sulfur compositions for use in acid copper plating baths which are prepared by reacting a mixture of
(a) a disulfide having the formula EQU [RR'NCS.sub.2 ].sub.2 (Formula I) PA0 wherein R and R' are each independently hydrogen, alkyl or aryl groups, and PA0 (b) a halo hydroxy sulfonic acid having the formula EQU X(CH.sub.2).sub.n CHOH--CH.sub.2 SO.sub.3 M (Formula II) PA0 wherein X is a halogen, n is one or two and M is hydrogen or an alkali metal, and PA0 (c) an aliphatic aldehyde having up to 3 carbon atoms in PA0 (d) an aqueous alkaline medium. PA0 (a) 2-thiazolidinethione and its lower alkyl derivatives, PA0 (b) water-soluble 2-imidazolidinethione and its lower alkyl derivatives, or PA0 (c) water-soluble reaction products of (a) or (b) with from about 1 to 10 moles of an alkyl aldehyde or dialdehyde and PA0 (A) one or more bath-soluble copper salts, PA0 (B) free acid, PA0 (C) chloride ions, PA0 (D) an effective amount of one or more bath-soluble nitrogen and sulfur-containing brightening compounds prepared by reacting a mixture of PA0 (a) a disulfide having the formula EQU [RR'NCS.sub.2 ].sub.2 (Formula I) PA0 wherein R and R' are each independently hydrogen, alkyl or aryl groups, PA0 (b) a halo hydroxy sulfonic acid having the formula EQU X(CH.sub.2).sub.n CH(OH)CH.sub.2 SO.sub.3 M (Formula II) PA0 wherein X is a halogen, n is one or two and M is hydrogen or an alkali metal, PA0 (c) an aliphatic aldehyde having up to three carbon atoms in, PA0 (d) an aqueous alkaline medium, and PA0 (E) one or more heterocyclic sulfur-nitrogen compounds selected from the group consisting of PA0 (e) 2-thiazolidinethione and its lower alkyl derivatives, PA0 (f) 2-imidazolidinethione and its lower alkyl derivatives, and PA0 (g) bath-soluble reaction products of (e) or (f) with an alkyl aldehyde or dialdehyde.
These compositions are effective particularly as leveling and brightening agents for acid copper plating baths, and when incorporated into copper plating baths, result in an improved level and bright copper deposit over a wide current density range.
In U.S. Pat. No. 3,798,138, acid copper plating baths are described which contain a mixture of (I) water-soluble organic leveling compounds which may be
(II) a brightener composition containing in its molecule (a) an acrylic carbon-sulfur group in which the carbon atoms is attached to at least one other hetero-atom selected from the group consisting of sulfur and oxygen and (b) a water-solubilizing group.